fuel cells systems analysis - energy

Fuel Cells Systems Analysis

R. K. Ahluwalia, X. Wang, K. Tajiri and R. Kumar

2010 DOE Hydrogen Program Review

Washington, DC

June 8-11, 2010

This presentation does not contain any proprietary, confidential, or otherwise restricted information.

Project ID: FC017

2

Overview

Timeline Start date: Oct 2003 End date: Open Percent complete: NA

BarriersB. CostC. PerformanceE. System Thermal and Water

ManagementF. Air ManagementJ. Startup and Shut-down Time,

Energy/Transient Operation

Budget FY10 funding: $650K (+$300K)

DOE share: 100% FY09 funding: $600K (+$300K)

Partners/Interactions Honeywell CEM+TWM projects DTI, TIAX 3M, Emprise, PermaPure ISO-TC192 WG12, HNEI,

JARI, LANL IEA Annexes 17 and 20 FreedomCAR fuel cell tech team

This project addresses system, stack and air management targets for efficiency, power density, specific power, transient response time, cold start-up time, start up and shut down energy

3

Objectives

Develop a validated system model and use it to assess design-point, part-load and dynamic performance of automotive and stationary fuel cell systems. Support DOE in setting technical targets and directing

component development Establish metrics for gauging progress of R&D projects Provide data and specifications to DOE projects on

high-volume manufacturing cost estimation

4

Approach

Develop, document & make available versatile system design and analysis tools. GCtool: Stand-alone code on PC platform GCtool-PSAT: Drive-cycle analysis of hybrid fuel cell

vehicles

Validate the models against data obtained in laboratory and at Argonne’s Fuel Cell Test Facility. Collaborate with external organizations

Apply models to issues of current interest. Work with FreedomCAR Technical Teams Work with DOE contractors as requested by DOE

5

Collaborations

Air Management Honeywell Turbo TechnologiesStack 3M, NuveraWater Management Honeywell Aerospace, Emprise, PermaPureThermal Management Honeywell Thermal SystemsFuel Economy ANL (PSAT)H2 Impurities HNEI, JARI, LANL, ISO-TC-192 WGSystem Cost DTI, TIAXDissemination IEA Annex 22 and 25

– Argonne develops the fuel cell system configuration, determines performance, identifies and sizes components, and provides this information to TIAX for high-volume manufacturing cost estimation

6

Technical Accomplishments1. System analysis to update the status of technology Stack: Determined the performance of NSTFC stacks with 0.15

mg/cm2 Pt loading and 20-µm membrane Air Management: Evaluated the performance of Honeywell’s

compressor-expander-motor module for 1.5-atm operation Fuel Management: Evaluated the performance of parallel ejector-

pump hybrids Water Management: Constructed performance maps for planar

membrane humidifiers Thermal Management: Collaborated with Honeywell to evaluate

performance of microchannel automotive radiators Drive Cycle Simulations: GCtool-PSAT simulations for fuel economy

of hybrid FCEVs Cost: Assisting TIAX in projecting cost of Argonne FCS-2010 at high

volume manufacturing2. Hydrogen impurity effects (Backup Slides) Conducting dynamic simulations to projected combined effect of H2

impurities at ISO specs Providing modeling support to ISO-TC192 WG-12 efforts

7

Argonne 2010 FCS Configuration

2010 FCSMEA- 3M NSTFC MEA- 20-µm 3M membrane- 0.05(a)/0.1(c) mg/cm2 Pt- Metal bipolar plates

AMS- Honeywell CEMM- Air-cooled motor/AFB

WMS- Cathode MH with precooler

TMS- Advanced 40-fpi

microchannel fins

FMS- Parallel ejector-pump hybrid

S1 – Pressurized FCS, 2.5 atm stack inlet pressure at rated power S2 – Low-pressure FCS, 1.5 atm stack inlet pressure at rated power S3 – S2 without cathode humidifier, HT coolant in pre-cooler

8

Air Management System Determined performance of Honeywell’s compressor-expander-

motor module (CEMM) originally designed for 2.5-atm peak P (S1) Comparable component efficiencies for S1 and S2 which may

improve with redesign for higher rpm

Mixed axial flow compressor

Variable nozzle turbine (VNT)

3-phase brushless DC motor, liquid and air cooled

Motor controller, liquid cooled

Air foil bearing (AFB)

0

20

40

60

80

100

0 20 40 60 80 100Mass Flow Rate (%)

Effic

ienc

y (%

) CompressorMotor

Expander

Motor Controller

30

50

70

90

110

Shaf

t Spe

ed (k

rpm

)

S1

S2

1.0

1.5

2.0

2.5

Dis

char

ge P

(atm

) S1

S2

9

Performance of Integrated CEM Module Maximum turndown may be limited by compressor surge for shaft

speeds less than 45 krpm At rated power, the CEMM consumes ~10 kWe in S1, <6 kWe in S2 CEMM min. power between 270-400 We, determined by AFB durability

1

10

100

30 40 50 60 70 80 90 100 110Shaft Speed (krpm)

Turn

dow

n S1

S2

Surge Limit

0

2

4

6

8

10

0 10 20 30 40 50 60 70 80FCS Net Power (kWe)

CEM

Pow

er (k

We)

S2

S1

10

Reference Stack with 3M’s NSTF Catalysts 3M’s single cell data with 0.1(a)/0.15(c) mg/cm2 Pt, ternary PtCoMn

catalyst, and 35-µm 850 EW membrane 3M’s single cell data with 0.05(a)/0.1(c) mg/cm2 Pt, ternary PtCoMn

catalyst, and 20-µm 850 EW membrane ECSA, specific activity, short and crossover currents and HFR data

from CV, EIS and H2/air cells at 0.9 V, 70-120oC, 20-100% RH Determined optimum combination of stack temperature and inlet RH

as a function of pressure, stoichiometry and MEA parameters

FCS S1 S2 S3

Stack P, atm 2.5 1.5 1.5

Stack T, °C 85 75 65

Dew Point T (c), °C 64 61 22

Dew Point T (a), °C 59 53 22

0.5

0.6

0.7

0.8

0.9

0.0 0.3 0.6 0.9 1.2 1.5 1.8Current Density (A/cm2)

Cel

l Vol

tage

(V)

0.0

0.3

0.6

0.9

1.2

Pow

er D

ensi

ty (W

/cm

2 )S2

S1

S3

S1

S2

S3

Cell Voltage

Power Density

11

Stack Performance – Effect of Pt Loading Reference 2009 S1 system: 0.25 mg-Pt/cm2, 35-µm membrane Reference 2010 S1 system: 0.15 mg-Pt/cm2, 20-µm membrane 30-45% projected reduction in Pt content because of lower Pt loading

and thinner membrane, 0.12-0.30 g-Pt/kWe(net)

500

1000

1500

mW

/cm

2

Power Density at Rated Power

0.15 mg-Pt/cm2

20-μm membrane

0.25 mg-Pt/cm2

35-μm membrane

0.1

0.2

0.3

0.4

40 45 50System Efficiency (%)

g-Pt

/kW

e

Pt Content on System Basis

0.15 mg-Pt/cm2

20-μm membrane

0.25 mg-Pt/cm2

35-μm membrane

12

Stack Performance – Effect of Operating Pressure S1 has higher power density and lower Pt content even though cell V

has to be 25-35 mV higher to compensate for larger parasitic power

550

600

650

700

750

mV

S1

S2

Cell Voltage at Rated Power

500

1000

1500

mW

/cm

2 S1

S2

Power Density at Rated Power

0.1

0.2

0.3

40 45 50System Efficiency (%)

g-Pt

/kW

e

S1

S2

Pt Content on System Basis

13

Fuel Management System Parallel ejector-pump hybrid Ejector performance

– Motive (p) gas: cH2, 15-atm maximum P, MW=2– Suction (s) gas: H2 with water, 1-1.5 atm, 75oC, MW=3-7– Lift pressure: <3 psi; Recycle ratio: ms/mp = 2-5 – Blower flow rate(%): 100-Entrainment(%)

0

20

40

60

80

100

120

0 20 40 60 80 100Power (%)

Entr

ainm

ent (

%)

0

3

6

9

12

15

18

Mot

ive

Gas

Pre

ssur

e (a

tm)

Ejector OnlyBlower OnlyEjector

+Blower

M > 1

M < 1

14

Alternate Arrangements A blower is always needed if the FCS has a turndown >3 with single

ejector, >4 with variable geometry ejector, and > 5 with dual ejectors

Dual Ejectors + Blower Variable Geometry Ejector + Blower

Blower None Single Variable Geometry Dual

Flow Rate L/s 20 5.6 4.5 3.1Pressure Head psi 3 0.8 0.65 0.4Power W 400 35 25 10

Ejector Arrangement

0

20

40

60

80

100

120

0 20 40 60 80 100Power (%)

Entr

ainm

ent (

%)

0

3

6

9

12

15

18

Mot

ive

Gas

Pre

ssur

e (a

tm)

Ejector 1 OnlyEjector 2 Only

Blower Only

E2+ B

M < 1

M > 10

20

40

60

80

100

120

0 20 40 60 80 100Power (%)

Entr

ainm

ent,

Thro

at A

rea

(%)

Ejector OnlyBlower Only Ejector+

BlowerEntrainment

Throat Area

15

Water Management System Analyzed Honeywell and PermaPure data for full-scale (FS), half-scale

(HS) and 1/10th sub-scale (SS) membrane humidifiers Permeance (κm) for the units (not local values) can be represented in

terms of the dry-air outlet RH. – κm defined similarly as LMTD for heat transfer– κm also depends on temperatures

Effectiveness (εm) can be represented in terms of NMTU (number of mass transfer units)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2 4 6 8 10 12 14 16NMTU

Effe

ctiv

enes

s

80C FS 90C FS80C HS 90C HS100% Flow SS 75% Flow SS25% Flow SS

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 20 40 60 80 100

RH of Humidified Air (%)

Perm

eanc

e (m

ol/m

2 .s.a

tm)

80C FS 90C FS

80C HS 90C HS

100% Flow SS 75% Flow SS

25% Flow SS

16

Water Mass Transfer Flux Model results for mass transfer from saturated wet stream Optimum dry-air inlet temperature (Tm) for maximum flux

– Flux decreases for Td > Tm because of low uptake (too dry)– Flux decreases for Td < Tm as humidified air approaches saturation

Flux is also a strong function of the membrane thickness, temperature of the wet air and operating pressures

0

1

2

3

4

5

6

7

8

45 55 65 75 85 95

Dry Air Inlet Temperature (oC)

Wat

er F

lux

(g/m

2 .s)

Membrane Thickness = 20 µmP = 2.5 atmWet Air T = 80oCWet Air RH = 100%

Approach TDP

5oC

10oC

15oC

35oC

17

Thermal Management System Heat rejection more difficult in FCVs than ICEVs

– Higher efficiency, but similar or higher heat loads but smaller ∆T– Additional FCS and electric drivetrain components requiring cooling

to lower temperatures: stacked A/C condenser, LTR and HTR– Heat rejection in FC powertrains is most challenging while driving at

55 mph on 6.5% grade with 600 kg payload– Allow stack temperature to rise when heat rejection is difficult– Expander needed even in S2 and S3

Rated Power kWe 80 80 80 80 80 80 80 80 80System Efficiency % 50 45 40 50 45 40 50 45 40Stack Pressure atm 2.5 2.5 2.5 1.5 1.5 1.5 1.5 1.5 1.5Stack Temperature oC 85 85 85 75 75 75 65 65 65Heat RejectionDemand Power kWe 61.5 61.5 61.5 61.5 61.5 61.5 61.5 61.5 61.5Cell Voltage mV 741 681 634 732 682 649 734 688 657Stack Pressure atm 2.4 2.4 2.3 2.1 2.1 2 2.1 2.1 2Stack Temperature oC 95 95 92 95 95 92 80 80 75HT Radiator Heat Load kW 49.5 59.5 68.3 49.3 57.6 63.5 49.4 56.7 62.2LT Radiator Heat Load kW 16.2 16.5 16.2 13.6 13.8 13.5 13.3 13.5 13.3

S1 S2 S3

18

Microchannel Radiator Derived f and j factors from Honeywell data for 9”x9”x1.3” subscale

and 27.6”x17.7”x1.3” full-scale radiators – 18 and 24 fpi louver and 40 and 50 fpi microchannel fins

FCS radiator can be more compact with 40-fpi microchannel than with standard automotive18-fpi louver fins

FC powertrains will likely be derated at Ta > 40oC since the fan power doubles for every 5oC increase in ambient temperature (Ta)

0

200

400

600

800

10 20 30 40 50 60 70 80 90 100HT Radiator Depth (mm)

Fan

Pum

ping

Pow

er (W

)

45°C (1.25)

MC-40Stack T: 95oCHeat Load: 56 kWVehicle Speed: 55 mph

Ambient T (A/Aref)

45°C (1.5)

40°C (1.25)

40°C (1.5)

19

Heat Rejection vs. Stack Efficiency at Rated Power

0

200

400

600

800

1000

60 70 80 90 100

Stack Temperature (oC)

Min

imum

Fan

Pum

ping

Pow

er (W

)

40%

45%50%

FCS Efficiency

MC-40A/Aref = 1.25Ambient T = 40oC

25

50

75

100

60 70 80 90 100

Stack Temperature (oC)

HT

Rad

iato

r Dep

th (m

m)

40%45%50%

FCS Efficiency

MC-40A/Aref = 1.25Ambient T = 40oC

At low stack temperatures, the minimum fan power increases nonlinearly with heat load (i.e., FCS efficiency at rated power)

For given fan power, 40% FCS (S2) must be capable of operating at 5-10oC higher stack temperature than 50% FCS

From the standpoint of heat rejection, 40% FCS may be acceptable if it can be operated at 95oC (S3 not OK)

20

System Performance - SummaryLowering rated-power efficiencyfrom 50% to 40% decreases peak efficiency by <1% fuel economy by 4% in battery-

charging mode (BCM) & 7% in load-following mode (LFM)

and system Pt content by 50%No. of start-stops on UDDS: 58 inBCM, 4 in LFM2

PSAT drive-cycle simulation results for a mid-size hybrid vehicle

48

49

50

51

52

53

54

55

56

BCM LFMUDDS

FCS

Effic

ienc

y (%

)

S2-3 (40%) S2-2 (45%) S2-1 (50%)

BCM LFMHWFET

BCM LFMLA92

70

72

74

76

78

80

82

84

86

88

BCM LFMUDDS

Fuel

Eco

nom

y (m

pgge

)

S2-3 (40%) S2-2 (45%) S2-1 (50%)

BCM LFMHWFET

50

52

54

56

58

60

62

64

66

68

BCM LFMLA92

BCM LFMCombined

20

25

30

35

40

45

50

55

60

0 10 20 30 40 50 60 70 80Power (kWe)

Effic

ienc

y (%

)

50%

45%

40%

21

Future Work1. Systems Analysis Support DOE/FreedomCAR development effort at system,

component, and phenomenological levels Collaborate with 3M to develop durability models for NSTFC

electrode structures Continue cooperation with Honeywell and others to validate air, fuel,

thermal, and water management models System optimization for cost, performance, and durability Drive cycle simulations for durability enhancement Alternate membrane, catalyst structures, and system configurations Support DTI and TIAX in high-volume manufacturing cost projections 2. Hydrogen Quality Validate impurity models against U.S. and JARI data Project effects of proposed standards on stack performance Provide modeling support to ISO-TC192 WG-12 and the Codes and

Standards Technical Team

27

Appendix

28

1. SMR-PSA may be the pathway for producing H2 in the early stages of hydrogen economy

CO and N2 levels determine the H2 recovery from PSA and influence the cost of producing H2

Of the two impurities, CO degrades the cell performance more but accumulation of N2 accumulation can significantly dilute the H2 concentration

Our simulations show that N2 crossover from air is the main source of N2 buildup in the anode recycle stream and determines the purge schedule

2. H2S and NH3 are extremely harmful to PEFC efficiency but are easily removed in PSA beds

Dynamic simulations show that NH3 cannot accumulate in the anode recycle stream

Dynamic Behavior of Fuel Hydrogen Impurities in Polymer Electrolyte Fuel Cells

29

Hydrogen Purification Drivers (PSA)

Relatively easier to remove

0.05 ppmStrongHalogenates


Dew PointDew Point5 ppmStrongWater (H2O)


0.004 ppmStrongTotal Sulfur


Low ppmLow ppm0.1 ppmStrongAmmonia


25000.5%5000.1 %2 ppm(incl CH4)

|Total HC’s


9000015 -18%8500015-17%2 ppm|Carbon Dioxide (CO2)

Impacts PSA recovery & Capital Cost

150000.5 – 3%100000.5 – 2%2 ppm(incl THC)

Methane (CH4)


2000000.1-4%500000.1 -1 %0.2 ppm|Carbon Monoxide (CO)


101000 ppm380034-38%100 ppm(total inert)

|Nitrogen (N2)


5500 ppm5500 ppm100 ppm(total inert)

|Argon (Ar)


--1050 ppm5 ppm|Oxygen (O2)


75-80%40-45%99.99%WeakHydrogen (H2)

NOT POSSIBLE5500 ppm5500 ppm100 ppm(total inert)

ZeroHelium (He)

OVERALLEFFECT

Purification Ratio for SMR

SMRMol %

Purification Ratio for ATR

ATRMol %

ISO TC 197 WG 12 (14687)

Draft Spec

Adsorption Force

Species


0.05 ppmStrongHalogenates


Dew PointDew Point5 ppmStrongWater (H2O)


0.004 ppmStrongTotal Sulfur


Low ppmLow ppm0.1 ppmStrongAmmonia


25000.5%5000.1 %2 ppm(incl CH4)

|Total HC’s


9000015 -18%8500015-17%2 ppm|Carbon Dioxide (CO2)


150000.5 – 3%100000.5 – 2%2 ppm(incl THC)

Methane (CH4)


2000000.1-4%500000.1 -1 %0.2 ppm|Carbon Monoxide (CO)


101000 ppm380034-38%100 ppm(total inert)

|Nitrogen (N2)


5500 ppm5500 ppm100 ppm(total inert)

|Argon (Ar)


--1050 ppm5 ppm|Oxygen (O2)


75-80%40-45%99.99%WeakHydrogen (H2)

NOT POSSIBLE5500 ppm5500 ppm100 ppm(total inert)

ZeroHelium (He)

OVERALLEFFECT

Purification Ratio for SMR

SMRMol %

Purification Ratio for ATR

ATRMol %

ISO TC 197 WG 12 (14687)

Draft Spec

Adsorption Force

Species

DOE H2QWG Draft Roadmap. Courtesy, Bhaskar Balasubramanian (Chevron)

30

CO/CO2 Poisoning Model

Hydrogen Oxidation Reaction

– H2 + 2M ↔ 2M-H (Dissociative Adsorption)

– M-H → M + H+ + e- (Electrochemical Oxidation)

CO Poisoning of Pt

– CO + M ↔ M-CO (Associative Adsorption on Linear Sites)

– CO2 + 2M-H → M + M-CO + H2O (Reverse Water-Gas Shift)

– M-CO + H2O → M + CO2 + 2H+ + 2e- (Electrochemical Oxidation)

Reactions with Oxygen

– M-CO + ½ O2 → M + CO2 (CO Oxidation)

– 2M-H + ½ O2 → 2M + H2O (H2 Oxidation)

31

H2S Poisoning Model

Sequential Sorption of H2S on Pt

1. nM + H2S ↔ Mn-H2S (Associative chemisorption)

2. Mn-H2S ↔ MnS + 2H+ + 2e- (Electrochemical reaction)

3. MnS + 3H2O → nM + SO3 + 6H+ + 6e- (Electrochemical oxidation)

Multi-site sorption of H2S, n is a function of total sulfur coverage (θS)

– n →1 as θS → 1, n → N as θS → 0

Near OC, MnS can re-convert to Mn-H2S (E2 = 0.14 V), and H2S can desorb for partial recovery

At a high anode overpotential (E3 = 0.89 V), MnS can oxidize to SO3, SO3 assumed completely soluble in water and removed from the system

32

Experimental Observations Reversible at low concentrations but may be irreversible at high

concentrations (Uribe 2002) CV traces suggest that NH3 is not significantly adsorbed on the

electrocatalyst (Uribe 2002 & Soto 2003). AC impedance spectroscopy data indicate that increased

membrane resistance cannot account for the observed overpotentials due to NH3 impurity (Soto 2003).

Model Transient stack model with steady-state option NH3 uptake in ionomer modeled as a reversible absorption-

desorption reaction Same approach for NH3 uptake in membrane except it is exposed

to both anode and cathode streams Effect of NH4

+ on conductivity from experimental data Postulated effect of NH4

+ on ORR kinetics

NH3 Poisoning Model

33

HCHO/HCOOH/C7H8 Poisoning Model

Hydrogen Oxidation Reaction

– H2 + 2M ↔ 2M-H (Dissociative Adsorption)

– M-H → M + H+ + e- (Electrochemical Oxidation)

Poisoning of Pt

– HCHO + M → M-CO + 2H++ 2e- (Dissociative Adsorption)

– HCOOH + M → M-CO + H2O (Dissociative Adsorption)

– C7H8 + M ↔ M-C7H8 (Associative Adsorption)

Reaction with Hydrogen

– C7H8 + 6M-H → 6M + C7H14 (Hydrogenation to MCH)

34

NH3 Impurity Model Development (JARI Data)

0

30

60

90

120

150

0.25 0.30 0.35 0.40 0.45 0.50

Anode/Cathode Pt Loading (mg/cm2)

DV (m

V)

T, Tdp = 80/77(a)/50(c)oCNH3 Conc. = 10 ppmUtiliization = 17(a)/40(c)%J = 1 A/cm2

Modeled NH3 crossover is a function of uptake and current density

0

10

20

30

40

0.0 0.2 0.4 0.6 0.8 1.0NH3 Concentration (ppm)

DV (m

V)

T, Tdp = 80/77(a)/50(c)oCPt Loading = 0.3 mg/cm2

Utiliization = 17(a)/40(c)%J = 1 A/cm2

Exposure Time = 10 h

35

HCHO/HCOOH Impurity Model Development:JARI Data

0

5

10

15

20

25

0 4 8 12 16 20HCHO Concentration (ppm)

DV (m

V)



0

5

10

15

20

0 100 200 300 400 500HCOOH Concentration (ppm)

DV (m

V)



36

Toluene alone: Small ∆V, significant conversion to methyl-cyclohexane Toluene + CO: Larger ∆V, insignificant hydrogenation

Analysis of HNEI Data: Toluene

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 20 40 60 80 100Time, h

Flow

Rat

e, n

mol

/s

CO In

A/C: 7/7psig, 2/2 Stoich 100/50% RH, H2/Air60oC2 ppm CO1 A/cm2

CO Out

CO2 Out

CO2 In

0

2

4

6

8

10

12

0 20 40 60 80 100Time, h

Flow

Rat

e, n

mol

/s

C7H8 In

A/C: 7/7psig, 2/2 Stoich 100/50% RH, H2/Air60oC20 ppm C7H8

1 A/cm2

C7H8 Out

C7H14 Out

0

100

200

300

400

0 20 40 60 80 100Time, h

DV, m

V

A/C: 7/7psig, 2/2 Stoich 100/50% RH, H2/Air60oC1 A/cm2

20 ppm C7H8

2 ppm CO

2 ppm CO + 20 ppm C7H8

0

2

4

6

8

10

12

0 20 40 60 80 100Time, h

Flow

Rat

e, n

mol

/s

C7H8 In

A/C: 7/7psig, 2/2 Stoich 100/50% RH, H2/Air60oC20 ppm C7H8+2 ppm CO1 A/cm2

C7H8 Out

C7H14 OutCO In CO2 Out

2-ppm CO

20-ppm C7H8

∆V

2-ppm CO +20-ppm C7H8

37

Effect of Inerts (N2, He, CH4) Giner data for N2 permeance as a function of T and membrane

water content (fv)– N2 crossover from cathode air may potentially exceed N2 in H2

He permeance from JARI data: 2.4x10-13 mol/cm.s.kPa at 80oC, 77oC dew point, 1.6 higher than H2 permeance

CH4 and CO2 are relatively impermeable (HNEI, JARI)

0.0E+00

2.0E-14

4.0E-14

6.0E-14

8.0E-14

1.0E-13

1.2E-13

1.4E-13

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35fv

Perm

eanc

e (m

ole/

cm.s

.kPa

)

95oC

80oC

60oC

30oC

38

1. Pressurized stack 87 kWe at 1 A/cm2 with pure H2

50% O2 & 70% per-pass H2 utilization N111 membrane, 0.2(c)/0.1(a) mg/cm2 Pt loading Stack pressure: 2.5/1.9/1.6 atm at 100/25/5% power Inlet RH: 60/80/90% at 100/25/5% power2. Purge criteria Single purge (14 L) equivalent to 2 volumes of anode subsystem

restores gas in anode channels to the H2 fuel specs 3. Definitions Concentrations generally reported as max. values after 30-h

exposure Stack efficiency defined as ratio of DC power produced to the LHV

of H2 consumed (chemically and electrochemically) and purged

Reference Conditions, Assumptions, Definitions

39

Dynamic simulations of Impurity Effects Purge occurs whenever impurity concentration reaches 15%

779

780

781

782

Cel

l Vol

tage

(V) 0.25 A/cm2

645

650

655

660

0 5 10 15 20 25 30Time (h)

Cel

l Vol

tage

(mV) 1 A/cm2

40

Purge Loss and Schedule

At low power, purge interval determined primarily by N2 crossover At high power, buildup of fuel impurities also affects purge interval

0

2

4

6

8

10

12

0 25 50 75 100Stack Power (%)

Purg

e Lo

ss (%

)

0

100

200

300

400

500

600

Purg

e In

terv

al, s

Purge Loss

Purge Interval

Pure H2

ISO H2

Pure H2

ISO H2

CO: 0.2 ppmCO2: 2 ppmN2: 100 ppmHe: 200 ppmNH3: 0.1 ppmHCHO: 10 ppbHCOOH:0.2 ppmC7H8: 2 ppmH2S: 4 ppb

41

Dynamic Pt Coverage

Steady-state coverage of CO & C7H8 functions of P & overpotentials No SS coverage for H2S which competes with CO & C7H8 for vacant sites

0

5

10

15

20

Cov

erag

e (%

)

CO

H2S

100% Power

C7H8

0

2

4

6

0 5 10 15 20 25 30Time (h)

Cov

erag

e (%

) CO

H2S

25% Power

C7H8

42

Buildup of Impurities with Dynamic Purge: N2, He, CO, CO2

0

5

10

15

N2 (

%)

Stack Inlet

Stack Outlet

0

1

2

3

4

He

(%)

Stack Inlet

Stack Outlet

0

150

300

450

600

0 20 40 60 80 100Stack Power (%)

CO

2 (pp

m)

Stack Inlet

Stack Outlet

N2 buildup almost entirely due to N2 crossover from cathode No buildup of CO as it is quantitatively converted to CO2

43

Dynamic Buildup of NH3, H2S and HCHO No buildup of NH3, NH3 crossover increases with current density H2S breakthrough at more than 20% power, >30 h exposure

0.00

0.05

0.10

NH

3 (pp

m) Stack Inlet

Stack Outlet

0

5

10

15

H2S

(ppb

)

Stack Inlet

Stack Outlet

0

5

10

15

20

0 20 40 60 80 100Stack Power (%)

HC

HO

(ppb

)

Stack Inlet

Stack Outlet

Enrichment

)1()1(

2H

ii

ini

outi

i

E

CCE

Φ−Φ−

=

=

44

Dynamic Buildup of HCOOH and C7H8

Slower dissociative adsorption of HCOOH than HCHO Conversion of toluene to methyl-cyclohexane slows at higher power

0

5

10

15

HC

OO

H (p

pm)

Stack Inlet

Stack Outlet

0.0

0.5

1.0

1.5

2.0

C7H

8 (pp

m) Stack Inlet

Stack Outlet

0

100

200

300

400

0 20 40 60 80 100Stack Power (%)

C7H

14 (p

pm)

Stack Inlet

Stack Outlet

45

Simultaneous Effect of Impurities

Losses defined with respect to cell voltage and stack efficiency for pure fuel hydrogen accounting for N2 crossover from cathode

At <30% power, ∆V approaches zero but 0.35 percentage point reduction in stack efficiency due to buildup of impurities

Slow increase in ∆V expected at longer exposure because of H2S uptake

0

5

10

15

0 20 40 60 80 100Stack Power (%)

DV (m

V)

0.00

0.25

0.50

0.75

1.00

Dh (%

)

DV

DhPt Loading: 0.1(a)/0.2(c) mg/cm2

Exposure Time: 30 hTemperature: 80oC

46

Effect of Anode Pt Loading

Substantially higher ∆V and ∆η with 0.05 mg/cm2 Pt (a) for >50% stack power

0

10

20

30

DV (m

V)

0.1 mg/cm2 Pt(a)

0.05 mg/cm2 Pt(a)Exposure Time: 30 hTemperature: 80oC

0.0

0.5

1.0

1.5

2.0

0 20 40 60 80 100Stack Power (%)

Dh (%

)

0.1 mg/cm2 Pt(a)

0.05 mg/cm2 Pt(a)

47

Effect of Stack Temperature

70oC stack temperature, 1.5 bar inlet pressure at rated power

0

10

20

30

DV (m

V)

70oCPt Loading: 0.1(a)/0.2(c) mg/cm2

Exposure Time: 30 h

80oC

0.0

0.5

1.0

1.5

2.0

0 20 40 60 80 100Stack Power (%)

Dh (%

)

70oC

80oC

48

Sensitivity Analysis Results for 100% stack power, ISO max impurity specs with one

species at 2X and 0.5 X concentration

0

5

10

15

20

25

CO CO2 N2 He NH3 HCHO HCOOH C7H8 H2S

DV (m

V)

Pt Loading: 0.1(a)/0.2(c) mg/cm2


0.0

0.5

1.0

1.5

2.0

CO CO2 N2 He NH3 HCHO HCOOH C7H8 H2S

Dh (%

)

49

Drive Cycle Simulations Multiple repeats of warm FUDS (1372 s) and FHDS (740 s) for 30 h Insignificant differences in VI curve for the last FUDS-FHDS cycle

0

1

2

3

4

5

Cov

erag

e (%

) CO

H2SC7H8

50

51

52

53

54

55

0 5 10 15 20 25 30Time (h)

Effic

ienc

y (%

)

Pure H2

ISO H2

Pt Loading: 0.1(a)/0.2(c) mg/cm2


50

Summary and Conclusions N2 crossover from air is the main source of N2 buildup in the anode

recycle stream and determines the purge schedule Dynamic simulations show that NH3 cannot accumulate in the anode

recycle stream– Significant crossover of NH3 to cathode air– Cumulative degradation in performance due to H2S

Cyclic buildup of formaldehyde, formic acid and methyl-cyclohexane Critical data needs

– CO/CO2: H2 pump data for independent verification of chemical vs. electrochemical CO oxidation

– NH3 crossover as function of current density, NH3 isotherms as functions of RH and T

– H2S: Isolation of anode vs. cathode overpotentials– Effect of T on behavior of HCHO, HCOOH and C7H8

fuel cells systems analysis - energy

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